First, Donald Trump threatened to pull the US out of NATO is member states didn’t fulfill their pledges to boost their defense spending. But that’s just a squabble about money. Now, he’s called into doubt America’s commitment to NATO’s collective security by questioning why the US should fight to defend Montenegro. “They’re an aggressive people,” Trump says, adding that an aggressive Montenegro could start World War 3. Montenegrins are insulted and bemused…NATO allies are worried. USA Today White House correspondent David M Jackson helps to sort things out.